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Did Mystery Object Rumble Our Monster Black Hole?

The supermassive black hole in the center of our galaxy has started to stir and astronomers are pondering whether the uptick in flare activity has been triggered by the passage of a mysterious dust-enshrouded star.

The supermassive black hole in the center of our galaxy has started to stir and astronomers are pondering whether the uptick in flare activity has been triggered by the passage of a mysterious dust-enshrouded star.

Until recently, the Milky Way's supermassive black hole - that resides in a region of our galaxy's core called Sagittarius A* - has been generating bright flares roughly once every 10 days. Over the past year, however, activity has increased and Sagittarius A* (or Sgr. A* for short) has been flaring roughly once per day.

Using data from 3 space telescopes, astronomers have been able to better understand these powerful flaring events and they may have found a fascinating cosmic connection.

"For several years, we've been tracking the X-ray emission from Sgr A*. This includes also the close passage of this dusty object," said Gabriele Ponti, of the Max Planck Institute for Extraterrestrial Physics in Germany, in a Chandra press release. "A year or so ago, we thought it had absolutely no effect on Sgr A*, but our new data raise the possibility that that might not be the case."

NASA's Chandra X-ray Observatory and ESA's XMM-Newton, with complementary data from NASA's Swift satellite, were used to piece together Sgr. A*'s activity as a dusty cloud approached the black hole. Discovered in 2011, astronomers were excited by the prospect of an object, called simply "G2″, would encounter Sgr. A*, and possibly be consumed after getting caught in the black hole's gravitational well. Had this happened, astronomers hoped to see a massive flare, giving humanity a wonderful glimpse into the high-energy processes erupting in a black hole's accretion disk and event horizon.

Alas, as G2 made close approach in 2014... nothing happened. At least, nothing obvious happened.

Before close approach, it was thought that G2 was most likely a cloud of dust and gas; possible stellar remnants idly orbiting through the galaxy's core. But after its supermassive encounter, G2 continued on its merry way, zooming around the black hole and orbiting back out into interstellar space. That's when G2′s nature became clear - it was probably a star, cocooned in a dusty envelope, whose gravity maintained its form and little of the cloud's material was allowed to be ripped away and fall into the black hole.

Although our supermassive black hole had the munchies, its G2 snack was ripped from its clutches.

No doubt extreme gravitational perturbations disrupted the star and associated cloud, but there was no evidence of any flaring activity, meaning G2 had escaped pretty much intact.

In new research accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, however, it seems that Sgr. A* has been the site of an uptick in flaring activity, a possible sign that some of the dust from G2 did indeed get pulled into the black hole, generating near-daily blasts of X-ray radiation.

"There isn't universal agreement on what G2 is," said Mark Morris of the University of California at Los Angeles. "However, the fact that Sgr A* became more active not long after G2 passed by suggests that the matter coming off of G2 might have caused an increase in the black hole's feeding rate."

Of course, correlation doesn't necessarily mean causation; there may be another explanation for the increase in flaring activity - if this increase is real at all.

It could be that stellar winds near the black hole have been feeding Sgr. A* with more material, causing an increase in activity. Or it could be that we have gotten better at detecting these X-ray flares and the daily flaring activity has only just been discovered in the data. But the possibility that G2 might be to blame is exciting as we could be getting one of the first looks into the cause and effect of an object messing with the feeding habits of a black hole.

"It's too soon to say for sure, but we will be keeping X-ray eyes on Sgr A* in the coming months," said co-author Barbara De Marco, also of Max Planck. "Hopefully, new observations will tell us whether G2 is responsible for the changed behavior or if the new flaring is just part of how the black hole behaves."

This month marks the 15th year that NASA's awe-inspiring Chandra X-ray Space Telescope has been observing high-energy phenomena in the cosmos. With its X-ray vision, the orbiting telescope has brought us some of the most mind-blowing views of supernova remnants -- the glowing embers of stars that have (in cosmic timescales) recently exploded, spewing out hot gas and dust. Shock waves traveling millions of miles an hour can still be observed ripping through these interstellar clouds.
Chandra's contribution to our understanding of the aftermath of a star's life has been nothing short of revolutionary, so to celebrate its 15 years in space,

Shown here is perhaps the most famous remnant of all. First observed by Danish astronomer Tycho Brahe over 400 years ago, this beautifully symmetric expanding cloud is a perfect example of a supernova remnant in action. Powerful shock waves can be seen within the supersonic gases traveling outward and inward, energizing the stellar material as it goes. The blue outer shell of X-ray emissions is caused by these outward-propagating shock waves accelerating electrons, whereas the red and green emissions are energized gases accelerated by the inwardly propagating shocks.

This eerie supernova remnant was spawned in 1181 AD by a supernova observed by Chinese and Japanese astronomers. By zooming in on the central region of the remaining cloud of debris, Chandra has been able to resolve the impact of the rapidly spinning neutron star that can be seen in its core. A torus of X-ray-generating material can be seen. X-ray jets can be seen accelerating away from the neutron star to the left and right. This turbulent mess of high-energy gases, shocks and powerful magnetic fields has generated X-ray emissions across the energy spectrum. High-energy X-rays are the bright blue regions; the redder regions are lower energy X-rays.

As with 3C58, the Crab Nebula also has a spinning neutron star in its core and Chandra has gotten up-close and personal with this stellar corpse. Created from super-dense material that has collapsed in on itself after the supernova explosion, neutron stars retain much of the original star's spin -- but as the neutron star is only a few miles wide, the smaller object spins much faster, often many times per second. If the conditions are right, the neutron star can generate bright X-ray and radio emissions, becoming a pulsar. In the center of the Crab Nebula is a very well-known pulsar that sports an energetic ring of material and impressive jets spouting from its poles. The exploding star that generated this pulsar and remnant exploded in 1054 AD and was recorded by Chinese astronomers.

The supernova remnant G292.0+1.8 is of particular interest to astronomers. One of only three remnants in our galaxy known to contain large quantities of oxygen, G292.0+1.8 is a source of elements heavier than hydrogen and helium. The high metalicity of debris clouds like these form the basis of metal-rich stars, planets and complex chemistry that forms the basis for life.